Wireless communications systems, including cellular phones, paging devices, personal communication services (PCS) systems, and wireless data networks, have become ubiquitous in society. To attract new customers, wireless service providers continually seek to improve wireless services cheaper and better, such as by implementing new technologies that reduce infrastructure costs and operating costs, increase handset battery lifetime, and improve quality of service (e.g., signal reception).
CDMA technology is used in wireless computer networks, paging (or wireless messaging) systems, and cellular telephony. In a CDMA system, mobile stations (e.g., pagers, cell phones, laptop PCs with wireless modems) and base stations transmit and receive data in assigned channels that correspond to specific unique codes. For example, a mobile station may receive forward channel data signals from a base station that are convolutionally coded, formatted, interleaved, spread with a Walsh code and a long pseudo-noise (PN) sequence. In another example, a base station may receive reverse channel data signals from the mobile station that are convolutionally encoded, block interleaved, and spread prior to transmission by the mobile station. The data symbols following interleaving may be separated into an in-phase (I) data stream and a quadrature (Q) data stream for QPSK modulation of an RF carrier. One such implementation is found in the 1xEV-DV version of the IS-2000 standard.
In a 1xEV-DV wireless network, two types of interference limit the performance of the forward link (i.e., transmission link from base station to mobile station). When the mobile station is close to the base station, same cell interference due to multi-path reflections is the predominant type of interference. When the mobile station is at the outer edge of the cell site, neighboring cell interference is the predominant type of interference. Same cell interference is directly related to the transmit power of the base station. Since both 1xEV-DO and 1xEV-DV base stations continuously transmit at maximum power for packet data users, same cell interference is extreme in 1xEV-DO and 1xEV-DV wireless networks.
In U.S. patent application Ser. No. 10/929,842, incorporated by reference above, the Applicants disclosed a method and an apparatus for canceling forward channel (or forward link) interference in a 1xEV-DV or 1xEV-DO mobile station using a single antenna. However, it not only the forward channel that experiences interference from packet data users. Current simulations have shown that a cell site that maintains data calls will be able to maintain a maximum of only about 2 or 3 voice calls and 2 or 3 data calls at the same time. This is due to the high transmit power of the mobile stations that are engaged in a data call. Thus, the mobile stations cause high amounts of interference on the reverse link, just as the base station causes high amounts of interference on the forward link.
Indeed it has been shown that one mobile station transmitting data at 307 Kbps on the reverse link would generate as much interference as 16 voice-call mobile stations. This situation is expected to get worse in Release D of the 1xEV-DV standard, wherein a reverse packet data channel has been added which will transmit at even higher power and even higher data rates. This is expected to cause much higher interference to the other users.
Therefore, there is a need in the art for an improved base station that is capable of canceling interference on the reverse channel. In particular, there is a need for a single antenna base station that is capable of canceling reverse channel interference caused by mobile stations that are engaged in packet data calls.